1. Field of the Invention
This invention relates to permanent magnet devices. More particularly, this invention relates to a device for producing a toroidal, solenoidal magnetic field confined to a toroid.
2. Description of the Prior Art
Many devices that employ magnetic fields have heretofore been encumbered by massive solenoids with their equally bulky power supplies. Thus, there has been increasing interest in the application of permanent-magnet structures for uses such as electron-beam focusing and biasing fields. Solenoids are common and have many practical and useful electrical and electronic applications as they furnish longitudinal magnetic fields for laboratory measurements, dc field biasing, particle beam focusing and so on. Solenoids are employed in devices such as extended interaction amplifiers, klystrons, travelling wave tubes, and magnetrons. Typically, solenoids are made of a long wire wound in a close packed helix forming a cylindrical tube.
The current demand for compact, strong, static magnetic field sources that require no electric power supplies has created needs for permanent magnet structures of unusual form. There has been increasing interest in applications using permanent magnet structures. A number of configurations have been designed and developed for electron beam guidance in mm/microwave tubes of various types: for dc biasing fields in millimeter wave filters, circulators, isolators, strip-lines; for field sources in NMR (nuclear magnetic resonance) imagers; and so on. In recent years, it has been possible to furnish a structure, shown in FIG. 1, made of permanent magnets rather than the variety of cumbersome electric current solenoids with their dependence on equally bulky power sources.
Likewise, radially-oriented toroidal magnets are well known in the permanent magnet art. Problems with fabricating radially-oriented toroidal magnets have also been overcome. See for example, the patent to Leupold, U.S. Pat. No. 4,592,889, entitled "Method and Apparatus For the Pressing and Alignment of Radially Oriented Toroidal Magnets," Leupold, U.S. Pat. No. 4,911,627, entitled "Apparatus for Fabrication of Permanent Magnet Toroidal Rings" and Leupold, U.S. Pat. No. 5,063,004, entitled "Fabrication of Permanent Magnet Toroidal Rings". The structure disclosed and claimed herein features a magnetic field confined within a toroid parallel to the longitudinal axis of the tubular working space, rather than in a radially-oriented toroidal magnet disclosed in those inventions. Similarly, Clarke, reissued U.S. Pat. No. 33,736 and the underlying U.S. Pat. No. 4,731,598, entitled "Periodic Permanent Magnet Structure With Increased Useful Field" disclose stacking a plurality of toroidal magnets in a device for focusing a charged particle beam along a beam path.
Toroidal solenoids of the electrical current type are still being fabricated and used. The main disadvantage of electrical solenoids is the need for a cumbersome and equally bulky power supply, which has been long recognized.
Those concerned with the development of solenoids have long recognized the need for a solenoid of the permanent magnet type, i.e. a solenoid that does not require electrical current. The present invention fulfills this need by providing a longitudinal, toroidal magnetic field without electrical currents.
Examples of high-intensity, compact permanent magnets may be found in the following references:
Leupold, U.S. Pat. No. 5,216,400, entitled "Magnetic Field Sources for Producing High-Intensity Variable Fields";
Leupold, U.S. Pat. No. 5,216,401, entitled "Magnetic Field Sources Having Non-Distorting Access Ports";
Leupold, U.S. Pat. No. 4,837,542, entitled "Hollow Substantially Hemispherical Permanent Magnet High-Field Flux Source for Producing a Uniform High Field"; and
Leupold, U.S. Pat. No. 4,839,059, entitled "Clad Magic Ring Wigglers".
Additionally, magnets of the type described herein may be found in the following references:
Leupold et. al., "Bulk Reduction and Field Enhancement in Periodic Permanent-Magnet Structures," IEEE Transactions On Electron Devices, Vol. ED-34, No. 8, Aug. 1987;
Leupold et. al., "Novel High-Field Permanent Magnet Flux Sources," IEEE Transactions On Magnetics, vol. MAG-23, No. 5, pp. 3628-3629, September 1987; and
Leupold et. al., "A Catalogue of Novel Permanent-Magnet Flux Sources," Paper No. W3.2 9th International Workshop on Rare Earth Magnets And Their Applications, pp. 109-123, August 1987, Bad Soden, Federal Republic of Germany.
Further, magnets that provide uniform magnetic fields may be found in my co-pending U.S. patent applications that are incorporated herein by reference:
U.S. Ser. No. 650,845, filed Feb. 5, 1991, entitled "High-Power Machinery with Toroidal Permanent Magnets;"
U.S. Ser. No. 654,476, filed Feb. 13, 1991, entitled "High-Power Electrical Machinery" and;
U.S. Ser. No. 709,548, filed Jun. 3, 1991, entitled "High-Field Permanent Magnet Flux Source."